1. Field of the Invention
This invention relates to a non-single-crystalline semiconductor layer on a substrate and a method of making the same, and more particularly to a non-single-crystalline semiconductor layer and a method of making the same which are of particular utility when employed in a semiconductor photoelectric conversion device which may be used as solar battery and a method of making the semiconductor photoelectric conversion device.
2. Description of the Prior Art
A semiconductor photoelectric conversion device using a non-single-crystalline semiconductor layer composed of amorphous or semi-amorphous semiconductor layers has now been taken notice of because the non-single-crystalline semiconductor layer may be formed thin, that is, the semiconductor material needed is small in amount and because the photoelectric conversion effeciency can be enhanced, as compared with a semiconductor photoelectric conversion device employing a single crystal or polycrystalline semiconductor.
A conventional non-single-crystalline semiconductor layer is usually formed of silicon. The non-single-crystalline semiconductor layer of silicon has a relatively high energy band gap as of 1.8 eV. Accordingly, the non-single-crystalline semiconductor layer of silicon which has the 1.8 eV energy band gap is not sensitive to a light of relatively long wavelength, such as an infrared ray. Therefor, such a non-single-crystalline semiconductor layer cannot be used for a photoelectric conversion device sensitive to the infrared ray which is suitable for use in optical communication systems. and alarm systems.
The following method has heretofore been proposed for forming a non-single-crystalline semiconductor layer on a substrate.
The substrate is disposed in a reaction chamber having a gas inlet and a gas outlet, and a mixture gas including at least a semiconductor material gas and a carrier gas is introduced into the reaction chamber in a state that a gas in the reaction chamber is exhausted through the gas outlet. An electromagnetic field is applied to the mixture gas to ionize it into a plasma, thereby to deposit a semiconductor material on the substrate. In this case, the atmospheric pressure in the reaction chamber is held below 1 atm and the substrate is maintained at a temperature lower than that at which the semiconductor material deposited on the substrate is formed as a crystalline semiconductor layer, thereby to obtain a desired non-single-crystalline semiconductor layer on the substrate.
With the conventional method, the substrate is usually disposed in that region of the reaction chamber in which the mixture gas plasma is produced. In this case, however, it is very difficult to form the mixture gas plasma homogeneously over the entire surface of the substrate in the reaction chamber because of the plasma forming mechanism.
Accordingly, the prior art method is defective in that the non-single-crystalline semiconductor layer formed on the substrate has many voids and is unhomogeneous in the direction of the plane of the semiconductor layer. Further, even if non-single-crystalline semiconductor layer are formed concurrently and individually on a number of substrates placed in the reaction chamber, the non-single-crystalline semiconductor layers are inevitably subject to dispersion in property; consequently, the conventional method is incapable of mass production of non-single-crystalline semiconductor layers of good quality.
Moreover, in the conventional method, the electromagnetic field for ionizing the mixture gas into a plasma is usually a DC electromagnetic field or a low-frequency electromagnetic field, so that the ratio in which the mixture gas is ionized into the plasma is very low, for example, below 1%.
Therefore, relatively much time is needed for forming a non-single-crystalline semiconductor layer to a required thickness on the substrate. Further, the mixture gas which is not ionized into a plasma is discharged without being used; this is a waste of the mixture gas. In general, a semiconductor hydride or halide gas is used as the semiconductor material gas in the mixture gas. For example, in the case of forming a non-single-crystalline semiconductor layer of silicon on the substrate, an SiH.sub.4 (silane) gas is used as the abovesaid semiconductor material gas. Such SiH.sub.4 gas is ionized into a plasma of silicon and a plasma of hydrogen. According to the prior art method, since the electric field for ionizing the mixture is a DC or low-frequency electric field, the plasma of hydrogen is small in mass and hence is relatively small in kinetic energy. On the other hand, the plasma of silicon is large in mass and hence is relatively large in kinetic energy. The fact that the kinetic energy of the plasma of silicon is large means that damage is imposed on a non-single-crystalline semiconductor Si layer in the course of its formation on the substrate while depositing thereon silicon. Further, the fact that the kinetic energy of the plasma of hydrogen is small means that it does not easily enter into the layer; therefore the effect of neutralizing dangling bonds in the layer is not sufficient.
Accordingly, the conventional method is incapable of making of non-single-crystalline, semiconductor layer of good quality.